For the past year, I’ve been learning about virtual machines (VMs). 

I’ve mostly been using VirtualBox on Windows 10 and Parallels on my Mac. A few weeks ago I thought it was time to also explore Windows Hyper-V. So, I turned it on.

Big mistake – activating Hyper-V deactivated my ability to run 64-bit VMs within Virtual Box.  This was a problem; I have a model instructional set of VMs set up on my classroom computer, for export and installation on the student computers, And I had about a week invested in creating them (installed software, settings, model networks. etc).

Now, I did the two things (activate Hyper-V), and then revisit my VirtualBox VMs about a week apart. So, it took me a bit of time (and googling) to figure out how to fix the problem.
Although I went in and turned off the Hyper-V features within Apps and Features > Program and Features > Turn Windows Features On or Off, I also ran PowerShell commands to make sure it couldn’t come back on when I next updated my classroom computer system. 

My lesson? The reason the two virtualization applications don’t work well together is that Hyper-V is a Type I hypervisor for Windows 10 – and VirtualBox is a Type II hypervisor running within Windows 10.